Size Effect Of Fracture Parameters Of Fully-graded Concrete And A Comparative Study For Model Ⅰ Crack Propagation Criterion Of Concrete

Two problems on the fracture of concrete were studied in this paper:1) size effect of fracture parameters of fully-grade dam concrete;2) the comparative study on model I crack propagation criterions of concrete. Many researches on size effect of the fracture parameters of concrete have been extensively delivered, both experimentally and theoretically. Nonetheless, as for the designated cases of dam concrete, the precedent is comparatively rare. Additionally, on account of the restrictions of experiment equipment and cost, the popularity to investigate the fracture parameters associated with fully-grade concrete is further diminished. According to the current studies, whether the fracture parameters such as fracture energy and double-.^fracture parameters have size effect is still controversial. It should also be noted that the dam concrete adopted in the previous study was principally prepared in laboratory, which was deemed incapable to reasonably reflect the actual fracture performance of dam concrete. Therefore, the dam concrete in this study derives from a dam project under construction in the southwest of China. The cast-in-situ wedge-splitting specimen has a maximum size of2250mm×2250mm×450mm, and with an initial notch depth ratio of0.40. Investigations on size effect have been conducted with respect to fracture parameters including double-K fracture parameters、 fracture energy GF as well as the critical crack tip opening displacement CTODc. Results demonstrate that there is pronounced size effect on each of these fracture parameters. However, with the specimen size increase to1500mm, namely the ratio of ligament and maximum diameter of aggregate becomes greater than6, double-K fracture parameters and fracture energy are size independent.But for CTODc, a linear increasing trend with the dimensional growth is found.It is noteworthy that a variety of crack propagation criterions have been proposed in accordance with different fracture mechanisms., and good calculation achieved. Nevertheless, the previous studies were basically focused on normal concrete, in which the brittleness is non-significant. While the property of concrete brittleness will be more significant with the concrete strength grade increase, under such conditions, the applicable scope and reliability of each crack propagation criterions are worth to be studied. Hence, in this paper, Three crack propagation criterions, which characterized by initial fracture toughness、maximum tensile stress and nil stress intensity factor at the tip of the crack, were introduced to derive the load-crack mouth opening displacement curves (P-CMOD) of three-point bending beams with different concrete strength. Based on the results, P-CMOD curves calculated using criterions of maximum tensile stress and nil stress intensity factor at crack tip are basically consistent, but different from the one calculated using criterion characterized by initial fracture toughness. The difference is more significant with the increase of the concrete strength. The results indicate that the crack propagation criterion characterized by initial fracture toughness is reasonable to describe the fracture behavious of concrete beams with different strength.